The present invention relates to the photodissociation of chemical compounds by electrolytic means, and more particularly to such molecular dissociation reactions in an electrolytic cell where the electrodes are doped iron oxide.
The Government has rights in this invention pursuant to Contract No. DE-AC03-76SF00098 awarded by the U.S. Department of Energy.
During the past several decades there has been considerable interest and intense research in photochemical dissociation of chemical molecules, especially water. These studies have generally centered around chlorophyl mediated reactions which involve complex multistep reactions to achieve the photodissociation of water and the synthesis of various organic compounds. As a general outgrowth of research in this area, some studies have been undertaken into simpler photochemical systems which are capable, or potentially capable, of catalytically mediating the dissociation of chemical compounds into their respective elements. In this regard, one area of interest has been the photocatalytic dissociation water into its respective elements, oxygen and hydrogen by means of electrolytic processes. In such processes, currents are induced in semi-conductor materials by photon irradiation, and these currents, often with the assistance of externally applied potentials, have achieved low rate of dissociation of water. Fujishima et al. reported in Nature 238, 37, 1972, that they achieved association, but only with the aid of an externally applied potential. F. T. Wagner et al. reported (J.Am.Chem.Soc.102, 5444) in 1980 the photo dissociation of water utilizing strontium titanate single crystals or polycrystalline powders thereof. A. J. Nozik in 1976 (App.Phys.Letters 29, 150), and K. Ohashi et al., in 1977 (Nature 266, 610) reported that when n-type SrTiO.sub.3 or TiO.sub.2, and p-type GaP or CdTe were used in an electrolytic cell as anode and cathode, respectively, and irradiated with ultraviolet energy, water was dissociated without using any externally applied electrical potentials.
H. Mettee et al. in 1981 (Solar Energy Mat. 4, 443) have reported that a p/n diode, consisting of single crystal p-type GaP and polycrystalline n-type Fe.sub.2 O.sub.3, splits water at relatively low quantum yields when such diode was irradiated with visible and near ultra-violet light.
Such techniques, however, either require the addition of an externally applied potential to accomplish the dissociation; or they require radiation in the ultra-violet region; or they require electrodes fabricated from scarce rare elements, or carefully and expensively produced single crystals.
Therefore it is of considerable interest to devise processes for the photodissociation of water, or for the photo induced hydrogenation of CO, or CO.sub.2 to produce hydrocarbons, etc., wherein the photo process relies upon visible light, does not require any externally applied electrical potentials, utilizes common, readily available electrode materials, and utilizes simple, and inexpensive fabrication techniques for the electrodes.